We examined the similarity of childhood environment (number of years living together in home of origin) and adult environment (current frequency of contact or personal meetings with the co-twin) to determine whether monozygotic twins may have had more similar environmental experiences than dizygotic twins (Kendler, 1983). Using logistic regression while controlling for zygosity, we tested, separately by sex, whether the mean score on environmental measures predicted pair concordance for all phenotypes.
